Physics – Geophysics
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....99.6425r&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. A4, p. 6425-6436
Physics
Geophysics
71
Airglow, Electron Density (Concentration), F Region, Interplanetary Magnetic Fields, Light Emission, Plasma Jets, Polar Caps, Convective Flow, Daytime, Electron Precipitation, Geophysics, Plasma Dynamics, Polar Cusps, Time Dependence
Scientific paper
Polar patches are regions within the polar cap where the F-region electron concentration and airglow emission at 630 nm are enhanced above a background level. Previous observations have demonstrated that polar patches can be readily indentified in Polar Anglo-American Conjugate Experiment (PACE) data. Here PACE data and those from complementary instruments are used to show that some polar patches form in the dayside cusp within a few minutes of the simultaneous occurrence of a flow channel event (short-lived plasma jets approximately 2 km/s) and azimuthal flow changes in the ionospheric convection pattern. The latter are caused by variations of the y-component of the interplanetary magnetic field. The physical processes by which these phenomena cause plasma enhancements and depletions in the vicinity of the dayside cusp and cleft are discussed. Subsequently, these features are transported into the polar cap where they continue to evolve. The spatial scale of patches when formed is usually 200 to 1000 km in longitude and 2 to 3 degs wide in latitude. Their motion after formation and the velocity of the plasma within the patches are the same, indicating that they are drifting under the action of an electric field. Occasionally, patches are observed to occur simultaneously in geomagnetic conjugate regions. Since some of these observations are incompatible with the presently-accepted model for patch formation involving the expansion of the high latitude convection pattern entraining solar-produced plasma, further modeling of the effects of energetic particle precipitation in the cusp, the consequences of flow channel events on the plasma concentrations, and the time dependence of plasma convection as a result of interplanetary magnetic field B(sub y) changes is strongly recommended. Such studies could be used to determine the relative importance of this new mechanism compared with the existing theory for patch formation as a function of universal time and season.
Baker Kile B.
Dudeney John R.
Pinnock Michael
Rodger Alan S.
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